Determining distances to globular clusters via the parallaxes of individual stars has the advantage that the distances are determined directly, without having to rely on another distance method as
an intermediate step in the distance ladder. In addition, parallaxes are not influenced by the reddening of the clusters.
In this paper, we take the cluster parallaxes from [1]} (hereafter VB21). VB21 determined mean parallaxes for 170 globular and outer halo star clusters by averaging
the cluster parallaxes of individual member stars from the Gaia EDR3 catalogue. Cluster members were selected based on the Gaia EDR3 proper motions and parallaxes.
VB21 also applied multi-gaussian mixture modeling to classify stars into cluster members and background stars and determined the mean cluster parameters and their errors over multiple realizations
of statistically created member catalogues. In order to account for possible magnitude, color
and position dependent biases in the Gaia catalogue, VB21 applied the parallax corrections of [2]} to the individual stellar parallaxes. However when
testing the derived cluster parallaxes against the literature distances that we derive further below, VB21 found that even after applying the Lindegren et al. corrections,
there is still a mean offset in the Gaia parallaxes. In particular, they found that the parallax corrections suggested by
[2]} might have been overcorrecting the Gaia EDR3 parallaxes by \(\Delta \varpi \sim 0.007\)  mas. VB21 also found evidence for spatially correlated small scale
systematic errors of order \(\epsilon _\varpi \sim 0.01\)  mas. We therefore subtract \(\Delta \varpi = 0.007\)  mas from the derived mean parallaxes to correct for the parallax bias. The
small-scale correlated errors were already taken into account by the parallax averaging procedure of VB21. We list the median distances \(D=1/\varpi \)  for clusters with
\(\varpi /\sigma _\varpi >10\)  in Table REF  to allow a comparison of the Gaia EDR3 parallax distances with the other distances that we derive.
When calculating mean cluster distances we use the data for all clusters and the parallax values directly as will be described further below.
